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Analysis of drug interactions with lipoproteins by high performance affinity chromatography

Abstract

High density lipoprotein (HDL), low density lipoprotein (LDL), and very low density lipoprotein (VLDL) are lipoproteins previously shown to bind many basic and neutral hydrophobic drugs in serum. These interactions impact the distribution, delivery, metabolism, and excretion of drugs and are important in determining drug activity, pharmacokinetics, and toxicity in the human body. Information about drug-lipoprotein interactions and the strength of these interactions can be useful in determining the distribution of drugs following administration. The research presented in this dissertation uses high performance affinity chromatography (HPAC) and packed columns to study binding of the drug propranolol to immobilized lipoproteins such as HDL, LDL, and VLDL. Through these studies, two types of interactions were identified between the lipoproteins and propranolol and verapamil. The first interaction has a relatively high affinity and likely involves binding of the drug by surface apolipoproteins. This high-affinity saturable interaction was stereoselective for LDL. HDL and VLDL did not exhibit stereoselectivity. The second type of interaction observed in each lipoprotein had a lower affinity involved partitioning of the drug into the non-polar core of lipoproteins. Additional work analyzing the theory and experimental conditions needed for the detection of multiple binding mechanisms in HPAC columns when using frontal analysis is also presented. This work focuses on the evaluation of binding models that incorporated both a saturable type of binding and a non-saturable interaction. These evaluations make it possible to determine the experimental conditions that would be required for detection of this type of multi-mode interaction. These studies demonstrate that HPAC is a useful tool in characterizing mixed-mode interactions, as can occur with complex particles like lipoproteins. The affinity columns containing immobilized lipoproteins allowed these studies to be conducted using the same column for hundreds of experiments with short analysis times. The combined result of these advantages was the ability to quickly obtain precise data over a variety of drug concentrations. The results of these experiments indicate that similar columns prepared with other lipoproteins or biological membranes can be used in similar HPAC binding studies.